Growth reactor for gallium-nitride crystals using ammonia and hydrogen chloride

ABSTRACT

The present invention in one preferred embodiment discloses a new design of HVPE reactor, which can grow gallium nitride for more than one day without interruption. To avoid clogging in the exhaust system, a second reactor chamber is added after a main reactor where GaN is produced. The second reactor chamber may be configured to enhance ammonium chloride formation, and the powder may be collected efficiently in it. To avoid ammonium chloride formation in the main reactor, the connection between the main reactor and the second reaction chamber can be maintained at elevated temperature. In addition, the second reactor chamber may have two or more exhaust lines. If one exhaust line becomes clogged with powder, the valve for an alternative exhaust line may open and the valve for the clogged line may be closed to avoid overpressuring the system. The quartz-made main reactor may have e.g. a pyrolytic boron nitride liner to collect polycrystalline gallium nitride efficiently. The new HYPE reactor which can grow gallium nitride crystals for more than 1 day may produce enough source material for ammonothermal growth. Single crystalline gallium nitride and polycrystalline gallium nitride from the HYPE reactor may be used as seed crystals and a nutrient for ammonothermal group III-nitride growth.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to U.S.Provisional Application Ser. No. 61/175,618 filed May 5, 2009, thedisclosure of which is incorporated by reference in its entirety.

This application is further related to the following U.S. and PCT patentapplications:

International Patent Application Serial No. PCT/US2005/024239, filed onJul. 8, 2005, by Kenji Fujito, Tadao Hashimoto and Shuji Nakamura,entitled “METHOD FOR GROWING GROUP III-NITRIDE CRYSTALS IN SUPERCRITICALAMMONIA USING AN AUTOCLAVE”;

U.S. Utility patent application Ser. No. 11/784,339, filed on Apr. 6,2007,by Tadao Hashimoto, Makoto Saito, and Shuji Nakamura, entitled“METHOD FOR GROWING LARGE SURFACE AREA GALLIUM NITRIDE CRYSTALS INSUPERCRITICAL AMMONIA AND LARGE SURFACE AREA GALLIUM NITRIDE CRYSTALS,”which application claims the benefit under 35 U.S.C. Section 119(e) ofU.S. Provisional Patent Application Ser. No. 60/790,310, filed on Apr.7, 2006, by Tadao Hashimoto, Makoto Saito, and Shuji Nakamura, entitled“A METHOD FOR GROWING LARGE SURFACE AREA GALLIUM NITRIDE CRYSTALS INSUPERCRITICAL AMMONIA AND LARGE SURFACE AREA GALLIUM NITRIDE CRYSTALS”;

U.S. Provisional Patent Application Ser. No. 60/973,662 , filed on Sep.19, 2007, by Tadao Hashimoto and Shuji Nakamura, entitled “GALLIUMNITRIDE BULK CRYSTALS AND THEIR GROWTH METHOD”;

U.S. Utility patent application Ser. No. 11/977,661, filed on Oct. 25,2007, by Tadao Hashimoto, entitled “METHOD FOR GROWING GROUP III-NITRIDECRYSTALS IN A MIXTURE OF SUPERCRITICAL AMMONIA AND NITROGEN, AND GROUPIII-NITRIDE CRYSTALS GROWN THEREBY”;

U.S. Provisional Patent Application Ser. No. 61/067,117, filed on Feb.25, 2008, by Tadao Hashimoto, Edward Letts, Masanori Ikari, entitled“METHOD FOR PRODUCING GROUP III-NITRIDE WAFERS AND GROUP III-NITRIDEWAFERS”;

U.S. Provisional Patent Application Ser. No. 61/058,900, filed on Jun.4, 2008, by Edward Letts, Tadao Hashimoto, Masanori Ikari, entitled“METHODS FOR PRODUCING IMPROVED CRYSTALLINITY GROUP III-NITRIDE CRYSTALSFROM INITIAL GROUP III-NITRIDE SEED BY AMMONOTHERMAL GROWTH”;

U.S. Provisional Patent Application Ser. No. 61/058,910, filed on Jun.4, 2008, by Tadao Hashimoto, Edward Letts, Masanori Ikari, entitled“HIGH-PRESSURE VESSEL FOR GROWING GROUP III NITRIDE CRYSTALS AND METHODOF GROWING GROUP III NITRIDE CRYSTALS USING HIGH-PRESSURE VESSEL ANDGROUP III NITRIDE CRYSTAL”;

U.S. Provisional Patent Application Ser. No. 61/131,917, filed on Jun.12, 2008, by Tadao Hashimoto, Masanori Ikari, Edward Letts, entitled“METHOD FOR TESTING III-NITRIDE WAFERS AND III-NITRIDE WAFERS WITH TESTDATA”;

U.S. Provisional Patent Application Ser. No. 61/106,110, filed on Oct.16, 2008, by Tadao Hashimoto, Masanori Ikari, Edward Letts, entitled“DESIGN OF FLOW-RESTRICTING DEVICE IN THE HIGH-PRESSURE VESSEL FORGROWING GROUP III NITRIDE CRYSTALS AND METHOD OF GROWING GROUP IIINITRIDE CRYSTALS”;

U.S. Provisional Patent Application Ser. No. 61/200,211, filed on Nov.24, 2008, by Edward Letts, Tadao Hashimoto, Masanori Ikari, entitled“METHOD FOR PRODUCING GAN NUTRIENT FOR AMMONOTHERMAL GROWTH”; whichapplications are incorporated by reference herein in their entirety asif put forth in full below.

BACKGROUND

1. Field of the Invention.

The invention is, in one instance, related to a production method of GaNor other group III-nitride crystals for use as nutrient or seed crystalsin the ammonothermal method. GaN crystals grown using the currentinvention can also be used for successive device fabrication.

2. Description of the Existing Technology.

(Note: This patent application refers to several publications andpatents as indicated with numbers within brackets, e.g., [x]. A list ofthese publications and patents can be found in the section entitled“References.”)

Gallium nitride (GaN) and its related group III alloys are the keymaterial for various opto-electronic and electronic devices such aslight emitting diodes (LEDs), laser diodes (LDs), microwave powertransistors, and solar-blind photo detectors. Currently LEDs are widelyused in cell phones, indicators, displays, and LDs are used in datastorage disc drives. The majority of these devices are grown epitaxiallyon heterogeneous substrates, such as sapphire and silicon carbide. Theheteroepitaxial growth of group III nitride causes highly defected oreven cracked films, which hinders the realization of high-end opticaland electronic devices, such as high-brightness LEDs for generallighting or high-power microwave transistors.

Most of the problems inherent in heteroepitaxial growth could be avoidedby instead using homoepitaxial growth. Single crystalline group IIInitride wafers can be sliced from bulk group III nitride crystal ingotsand then utilized for high-end homoepitaxial growth of optical andelectronic devices. For the majority of devices, single crystalline GaNwafers are desired because it is relatively easy to control theconductivity of the wafer, and GaN wafers will provide the smallestlattice/thermal mismatch with device layers. However, the GaN wafersneeded for homoepitaxial growth are currently expensive compared toheteroepitaxial substrates. This is because GaN wafers are currentlyproduced with quasi-bulk growth method in which a thick layer of GaN isgrown with hydride vapor phase epitaxy (HYPE) on a heteroepitaxialsubstrate followed by removal of the substrate. Due to an open reactorconfiguration for HYPE, the growth efficiency is not as high as theconventional bulk growth method used for other semiconductor materialssuch as Si and GaAs.

Although a “real” growth method of bulk GaN is ideal, it has beendifficult to grow group III nitride crystal ingots due to their highmelting point and high nitrogen vapor pressure at high temperature.Growth methods using molten Ga, such as high-pressure high-temperaturesynthesis [1,2] and sodium flux [3,4], have been proposed to grow GaNcrystals. Nevertheless the crystal shape grown using molten Ga is a thinplatelet because molten Ga has low solubility of nitrogen and a lowdiffusion coefficient of nitrogen.

The ammonothermal method, which is a solution growth method, is apromising alternative for bulk GaN growth and has been demonstrated togrow real bulk GaN ingots [5]. High-pressure ammonia, which has hightransport speed and high solubility of GaN, is used as a fluid medium togrow bulk GaN. State-of-the-art ammonothermal method [6-8] requires asufficient supply of source material. While pure Ga metal can be used asa source material, it provides an uneven growth rate as the surface ofthe Ga nitridizes. To provide a more stable growth rate, polycrystallineGaN is desirable as a starting material.

One method to produce GaN polycrystals is direct nitridization of Gawith ammonia [9]. Nevertheless, this method can only yield powder formof GaN (i.e. microcrystalline or nanocrystalline).

On the other hand, HVPE which utilizes gaseous ammonia, gaseous hydrogenchloride and metallic Ga is commonly used to produce GaN wafers forsuccessive device fabrication. We found that HVPE can be applied toproduce source materials for the ammonothermal method.

With HYPE, single crystalline GaN seed can be grown on a main susceptorand parasitic polycrystalline GaN deposited inside the reactor can alsobe used as a nutrient for the ammonothermal growth. However, the currentHVPE reactors are designed to grow GaN for relatively short duration,typically for between 1 and 10 hours. In order to apply HYPE to producesource materials for the ammonothermal method, the reactor must bemodified to extend growth duration.

SUMMARY OF THE INVENTION

One of the major limitations in extending growth duration of HVPE isclogging in the exhaust system by powder formation. The powder is mainlycomposed of ammonium halide such as ammonium chloride. To avoid cloggingin the exhaust system, a second reaction chamber is added after a mainreactor or first reactor chamber where GaN is produced. In the secondreaction chamber, ammonium chloride formation may be enhanced and theammonium chloride may be collected efficiently. To avoid ammoniumchloride formation in the main reactor, the connection or “transitionzone” between the main reactor and the second reaction chamber ismaintained at elevated temperature. In addition or alternatively, thesecond reaction chamber may have two, three, or more exhaust lines whichcan be switched automatically to avoid overpressure of the system byclogging. These features together with details explained below helpsolve a clogging problem in the exhaust line of HVPE to extend theuninterrupted growth duration.

The reactor may be a vertical HVPE reactor or a horizontal HVPE reactor.

The substrate on which GaN or other III-V nitride material is depositedmay be a material other than GaN or other than the III-V nitridematerial being deposited, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 An schematic drawing of HVPE reactor.

-   -   1) Carrier gas inlet    -   2) Ammonia gas inlet    -   3) Hydrogen chloride gas inlet    -   4) Bottom flange of the main reactor    -   5) O-ring    -   6) Sheath tube    -   7) Ga container    -   8) Furnace for GaCl synthesis    -   9) PBN sheath to collect polycrystalline GaN    -   10) Seed for single crystalline GaN growth    -   11) Diameter for the growth region to measure cross sectional        area    -   12) Furnace for GaN growth    -   13) Susceptor    -   13 a) Shaft of the susceptor    -   14) Main reactor made of quartz tube    -   14 a) End flange of the quartz tube    -   15) O-ring    -   16) Clamp    -   17) Diameter of the second reaction chamber to measure the cross        sectional area    -   18) Valves    -   18 a) First valve    -   18 b) Second valve    -   19) Second reaction chamber    -   19 a) Volume of the second reaction chamber    -   20) Baffles    -   21) Transition zone

DETAILED DESCRIPTION OF THE INVENTION

In the following description of the preferred embodiment, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown by way of illustration a specific embodiment in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention. For instance, whileGaN may be formed in a method and reactor as discussed herein, othergroup III-nitride compounds may be formed, such as AlGaN or InGaN.

TECHNICAL DESCRIPTION OF THE INVENTION

The present invention in one instance provides a reactor design toproduce polycrystalline GaN nutrient and single crystalline GaN seedsfor the ammonothermal growth of group III-nitride crystals, primarilygroup III-nitride single crystals that include at least the element Gawith the possible addition of another group III elements B, Al, and In,such as Al_(x)Ga_(1−x)N or In_(x)Ga_(1−x)N (0≦x<1), orAl_(x)In_(y)Ga_(1−x−y)N (0<x<1, 0<y<1). The group III-nitride ingots aregrown by the ammonothermal method which utilizes high-pressure NH₃ as afluid medium, nutrient containing group III elements, and seed crystalsthat are group III-nitride single crystals. The high-pressure NH₃provides high solubility of the nutrient and high transport speed ofdissolved precursors. The ammonothermal growth requires a steady supplyof a nutrient, such as Ga metal or GaN. A polycrystalline GaN source hasthe benefit of providing improved growth rate stability compared to Gametal. Also, the ammonothermal growth requires single crystalline GaNseeds to initiate growth.

One method to produce polycrystalline GaN and single crystalline GaNsuitable for the source material of the ammonothermal growth is the HVPEmethod. Nevertheless, HVPE is traditionally used for growing epitaxialfilm up to several hundreds of microns. Since the typical growth rate ofGaN in HVPE is 50-150 μm/h, the growth reactor is designed to continuegrowth for up to ˜10 hours. In order to produce GaN source forammonothermal growth, however, HYPE reactor must be operated for longerduration. If HVPE reactor in the current technology were operated forover 24 hours, the exhaust line would be clogged with ammonium chloride.Also, injection nozzle of source gases (i.e. ammonia and galliumchloride) would be clogged unless the nozzle is properly designed.

To solve the above-mentioned problem, the current invention discloses anew design of HVPE reactor. To avoid clogging in the exhaust system, asecond reaction chamber is added after a main reactor where GaN isproduced. The second reaction chamber will enhance ammonium chlorideformation and the powder is collected efficiently in it. To avoidammonium chloride formation in the main reactor, the connection betweenthe main reactor and the second reaction chamber is maintained atelevated temperature. In addition, the second reaction chamber has twoor more exhaust lines, such as three or four or five or six exhaustlines. If one exhaust line is clogged with powder, the valve for analternative exhaust line will open and the valve for the clogged line isclosed to avoid overpressure of the system.

A reactor design in accordance with the current invention is explained.These features and other details are explained below together with theFIG. 1.

The HVPE reactor in FIG. 1 is a vertical type reactor with source gasinlets located at the bottom and exhaust lines located at the top. TheHYPE reactor consists of a main reactor made of quartz tube 14) and asecond reaction chamber made of stainless steel 19).

The bottom end of the main reactor is capped with a bottom flange 4).The bottom flange 4) has carrier gas inlet 1), ammonia gas inlet 2) andhydrogen chloride gas inlet 3).

The main reactor 4) is surrounded with a furnace for GaCl synthesis 8)and a furnace for GaN growth 12). The hydrogen chloride inlet isconnected to a Ga container 7) where GaCl_(x) (x=1, 2 or 3) issynthesized. GaCl_(x) is successively supplied to the seed crystalthrough an appropriate gas nozzle. Carrier gas such as nitrogen and/orhydrogen is fed through a sheath tube 6) in order to help isolate theammonia flow and the GaCl_(x) flow until the gases meet at the seedsurface.

To grow single crystalline GaN, a seed crystal 10) is mounted face-downon a susceptor 13). The susceptor 13) helps to achieve uniformtemperature over the surface of the seed crystal 10) so that singlecrystalline GaN is uniformly grown on the seed crystal 10).

The height of the susceptor 13) can be raised with a rod 13 a) duringthe growth process so that the location of the growth front on the seedis maintained at the same level. Also, the susceptor 13) can be rotatedby rotating the rod 13 a) to improve uniformity of gas supply andtemperature.

The main reactor 14) is lined with a PBN sheath 9) which extends to apoint lower than the mixing point of the gases, so that any parasiticdeposition of polycrystalline GaN occurs on the PBN sheath 9). In thisway, polycrystalline GaN nutrient can be collected efficiently on thePBN sheath 9).

Baffles 20) are located in a transition zone 21) of the reactor abovethe susceptor 13). The baffles reduce the amount of heat transferredfrom the main or first reactor chamber into the second reactor chamber.The baffles 20) also prevent the ammonium chloride powder from fallingback to the main reactor 14) from the second reaction chamber 19).Although there are holes in the baffles to let gas through, the holes insuccessive baffles are preferably offset such that the baffles do notprovide a direct optical path from the second reactor chamber to thefirst. The baffles are preferably positioned in or adjacent to theheated zone so that the temperature is sufficiently high to avoiddeposition of ammonium chloride.

The upper end of the quartz tube for the main reactor 14) may have awide end flange 14 a) which meets the flange of the second reactionchamber 19). The O-ring is preferably located sufficiently far from thecenter of the reactor so that the connection between the main reactor14) and the second reaction chamber 19) can be maintained at atemperature above 200° C., preferably above 350° C. If necessary, theO-ring can be cooled with air or fluid.

Since the sublimation temperature of ammonium chloride is 338° C.,ammonium chloride powder deposition on the connection or transition zonecan be avoided in this design. The residual gas is introduced into thesecond reaction chamber 19) without forming ammonium chloride powder inthe main reactor 14).

In the second reaction chamber 19), on the other hand, formation ofammonium chloride powder is enhanced because the gas slows down andcools down. To increase residence time of the gas, the cross section(measured at 17) of the second reaction chamber is set larger than thatof the main reactor (measured at 11). The second reaction chamber 19)can have fins or baffles which act as a powder collector and/or helppowder settle from the gas stream.

The second reaction chamber 19 has more than one exhaust line. In FIG.1, one exhaust line with isolation valve 18 a is initially used and theisolation valve 18 b) in the exhaust line is closed. When ammoniumchloride powder builds up in the first exhaust line and the reactorpressure exceeds a certain limit, the isolation valve 18 b) opens toswitch the exhaust path from the first line to the second line. Thesystem can have more than 2 exhaust lines so that growth can becontinued for a longer duration.

The HVPE reactor with the second reactor chamber disclosed herein avoidsdeposition of ammonium chloride in the main chamber. The second reactorchamber enhances formation of ammonium chloride powder and collects itefficiently so that clogging of the exhaust line is avoided. Inaddition, multiple exhaust lines with automatic valve switching furtherextends growth duration without interruption by clogging.

ADVANTAGES AND IMPROVEMENTS

The present application discloses a new HVPE reactor which, in someembodiments, can be operated more than 24 hours. Uninterrupted longgrowth of GaN in HVPE can produce single crystalline seed of sufficientthickness together with enough polycrystalline GaN to use inammonothermal growth of group III-nitride crystals. Since both singlecrystalline and polycrystalline GaN are used as source material for theammonothermal growth, the process is quite efficient. The currentinvention will therefore enable improvements in productivity of GaN bulkcrystals by the ammonothermal method.

REFERENCES

The following references are incorporated by reference herein:

[1]. S. Porowski, MRS Internet Journal of Nitride Semiconductor, Res.4S1, (1999) G1.3.

[2] T. Inoue, Y. Seki, O. Oda, S. Kurai, Y. Yamada, and T. Taguchi,Phys. Stat. Sol. (b), 223 (2001) p. 15.

[3] M. Aoki, H. Yamane, M. Shimada, S. Sarayama, and F. J. DiSalvo, J.Cryst. Growth 242 (2002) p.70.

[4] T. Iwahashi, F. Kawamura, M. Morishita, Y. Kai, M. Yoshimura, Y.Mori, and T. Sasaki, J. Cryst Growth 253 (2003) p. 1.

[5] T. Hashimoto, F. Wu, J. S. Speck, S. Nakamura, Jpn. J. Appl. Phys.46 (2007) L889.

[6] R. Dwilińiski, R. Doradzitiski, J. Garczyńiski, L. Sierzputowski, Y.Kanbara, U.S. Pat. No. 6,656,615.

[7] K. Fujito, T. Hashimoto, S. Nakamura, International PatentApplication No. PCT/US2005/024239, WO07008198.

[8] T. Hashimoto, M. Saito, S. Nakamura, International PatentApplication No. PCT/US2007/008743, WO07117689. See US20070234946, U.S.application Ser. No. 11/784,339 filed Apr. 6, 2007.

[9] H. Wu, J. Hunting, F. DiSalvo, M. Spencer, Phys. Stat. Sol. (c), 2No. 7 (2005) p. 2074.

Each of the references above is incorporated by reference in itsentirety as if put forth in full herein and particularly with respect todescription of methods of growth using ammonothermal methods and usinggallium nitride substrates.

CONCLUSION

This concludes the description of the preferred embodiment of theinvention. The following describes some alternative embodiments foraccomplishing the present invention.

In the preferred embodiment, specific design of growth apparatuses ispresented. However, other constructions or designs that fulfill theconditions described herein will have the same benefit as the example.

In the preferred embodiment, a vertical reactor with a face down seed isexplained. However, a vertical reactor with a face up seed, a horizontalreactor with a face up or down seed, or any other reactor design thatfulfill the conditions described herein will have the same benefit asthe example.

The present invention does not have any limitations on the size of thereactor or the amount recycled or grown, so long as the same benefitscan be obtained.

The foregoing description of the preferred embodiment of the inventionhas been presented for the purposes of illustration and description. Itis not intended to be exhaustive or to limit the invention to theprecise form disclosed. Many modifications and variations are possiblein light of the above teaching. It is intended that the scope of theinvention be limited not by this detailed description, but rather by theclaims appended hereto.

The appended claims are incorporated by reference into the specificationin their entirety and therefore are as much of a discussion of theinvention as the text above.

1. (canceled)
 2. A method of growing a group III-nitride materialcomprising (a) contacting ammonia vapor and at least one groupIII-halide gas in a reaction chamber of a reactor; (b) epitaxiallydepositing the group III-nitride crystalline material onto a firstsubstrate in a first reactor zone, producing an exhaust gas comprisingan ammonium halide that passes to a transition zone of the reactor; (c)maintaining the exhaust gas in the transition zone at a temperaturesufficient to maintain the ammonium halide in gas phase; (d) removingthe exhaust gas from the transition zone and into a second zone of thereactor, the second zone having a temperature at which solid ammoniumhalide precipitates from the exhaust gas to form a depleted exhaust gas;and (e) exhausting the depleted exhaust gas through a first exhaust-gasoutlet.
 3. A method according to claim 2 and further comprising (a)monitoring at least one of the flow rate and the pressure of the gas inthe reaction chamber, transition zone, the second zone, and/or the firstexhaust-gas outlet, and (b) exhausting the depleted exhaust gas througha second exhaust-gas outlet when the flow rate decreases below a minimumflow rate or the pressure exceeds a maximum pressure or both.
 4. Amethod according to claim 2 wherein the first substrate and depositionconditions are selected to produce single crystal group III-nitridematerial.
 5. A method according to claim 4 wherein the first substrateitself comprises the group III-nitride material being deposited.
 6. Amethod according to claim 4 wherein the first substrate comprisessapphire.
 7. A method according to claim 2 wherein the method furthercomprises depositing polycrystalline group III-nitride material on asecond substrate.
 8. A method according to claim 7 wherein the secondsubstrate comprises pyrolytic boron nitride.
 9. A method according toclaim 2 and further comprising adjusting a position of the firstsubstrate within the reactor during operation to move the firstsubstrate toward or away from the flow of the ammonia vapor and thegroup III-halide gas.
 10. A method according to claim 9 wherein theposition of the first substrate is adjusted at a rate that maintainsgrowth of the group III-nitride at about the same position within thereactor.
 11. A method according to claim 2 wherein the method furthercomprises rotating the first substrate during deposition.
 12. A methodaccording to claim 2 wherein the method further comprises reacting agroup III metal, alloy, or compound with a hydrogen halide gas withinthe reactor to form the group III-halide gas.
 13. A method according toclaim 12 and further comprising introducing a carrier gas with the groupIII-halide gas.
 14. A method according to claim 13 wherein the carriergas comprises nitrogen and/or hydrogen.
 15. A method according to claim2 wherein the ammonia gas is physically separated from the groupIII-halide gas in the reactor into the vicinity of the first substrate.16. A method according to claim 15 wherein the ammonia gas is physicallyseparated from the group III-halide gas in the reactor past a portion ofa second substrate.
 17. A method according to claim 2 wherein the groupIII element comprises gallium.
 18. A method according to claim 17wherein the halide comprises chloride.
 19. A hydride vapor phase epitaxyreactor for growing a group III-nitride crystalline material, comprising(a) a reactor body formed of a material compatible with reactants forgrowing the group III-nitride crystalline material; (b) a first gasinlet for introducing a first reactant comprising a halide gas; (c) asecond gas inlet for introducing a second reactant comprising ammonia;(d) a stand in a first reactor zone in a chamber of the reactor body tohold a substrate upon which the group III-nitride crystalline materialis grown; (e) a transition zone downstream of the stand; (f) a secondreactor zone downstream of the transition zone; and (g) one or moreheaters positioned and configured to heat the first reaction zone andthe transition zone but not the second reactor chamber to a temperatureabove the precipitation temperature of ammonium halide, such that theammonium halide precipitates in the secondary reactor chamber duringoperation. 20-26. (canceled)
 27. A hydride vapor phase epitaxy reactoraccording to claim 19 wherein the reactor has a removable liner forgrowing polycrystalline group III-nitride material in and removing saidmaterial from the reactor.
 28. A hydride vapor phase epitaxy reactoraccording to claim 27 wherein the removable liner comprises pyrolyticboron nitride.
 29. A hydride vapor phase epitaxy reactor according toclaim 19 wherein the second reactor zone has a cross-sectional area in adirection of gas flow that is sufficiently large to allow precipitatedammonium halide to settle and form a depleted exhaust gas.
 30. A hydridevapor phase epitaxy reactor according to claim 19 wherein the secondreactor zone has a reservoir sufficiently large to collect settledprecipitated ammonium halide. 31-35. (canceled)
 36. The reactor of claim19 wherein; (a) The first reactor zone is constructed with a quartztube, (b) The reservoir is constructed as a metal chamber, (c) Thequartz tube and the metal chamber are connected with an O-ring-sealedflange, (d) The location of the O-ring is separated from the waste gasstream by a sufficient distance that the temperature of the walltouching the waste gas stream is maintained higher than 200° C. inoperation.
 37. The reactor of claim 36, wherein the O-ring is separatedfrom the waste gas stream by a sufficient distance that the temperatureof the wall touching the waste gas stream is maintained higher than 350°C. in operation.
 38. The reactor of claim 36, wherein the O-ring iscooled with air or fluid.
 39. The reactor of claim 30, wherein thereservoir has more than one isolation valve.
 40. The reactor of claim39, wherein overpressure of the reservoir is avoided by automaticswitching of the isolation valves. 41-43. (canceled)
 44. The reactor ofclaim 30, wherein the reactor has plural plates with openings locatedbetween the crystallization zone and the reservoir, the openings of theplates are offset to not provide a direct optical path from thecrystallization zone to the reservoir, and the plates are located in aposition where the temperature is between 300° C. to 700° C. inoperation.
 45. The method of claim 17, wherein the growth is continuedwithout interruption for more than 1 day. 46-60. (canceled)